It is known that, in the motor vehicles driven by a liquid-cooled internal-combustion engine, the quantity of heat transferred by the engine to the liquid coolant is progressively given off to the environmental air by the intermediary of a radiator. The latter consists of a bundle of tubes having more or less crowded gills, the liquid coolant flowing inside the tubes, whereas the air which flows across the tube bundle sweeps the tubes externally.
It is likewise known that, at a determined point of the loop, for example at the outlet from the engine, the temperature of the liquid coolant is maintained to a certain value (selected beforehand as an optimum for the operation of the engine concerned) because the liquid flow loop comprises, in addition to the engine, the radiator and a circulation pump, also thermostatically controlled valve.
The latter valve reduces the rate of flow of the liquid flowing through the radiator as the temperature tends to drop with respect to the preselected value, and increases such rate of flow in the contrary instance: consequently, the quantity of heat transfered from the liquid to the environmental air is reduced or is increased, respectively.
Generally speaking, therefore, the rate of flow of the air which flows across the radiator tube bundle is not modified.
It is known that such a rate of flow of air is unusually generated by virtue of the fact that the radiator is arranged crosswise in a compartment internally of the vehicle, said compartment having one or more air-intake ports arranged in a pressural area of the aerodynamic field which surrounds the vehicle, and one or more air outlet ports arranged in a negative pressure area or, anyhow, in an area in which a pressure obtains which is smaller than that obtaining at the air intake ports.
By so doing, the rate of flow of the air is virtually proportional to the vehicle advance speed: at low speeds, especially under certain particular conditions of environment and use, the rate of flow of the air is generally inadequate. In order that the rate of flow of air may be matched to the requirements inherent in such conditions of use, the magnitude of the rate of flow of air is generally increased by means of a specially provided fan.